This invention relates generally to track apparatus for vehicles. In particular, this invention relates to track apparatus of the type for use in place of a vehicle wheel and, more particularly, to apparatus for driving the flexible tracks of such apparatus during vehicle operation.
Agricultural vehicles such as tractors, combines and the like are commonly used in agricultural fields for a variety of jobs, and construction vehicles and other large work vehicles are used for many different jobs on a variety of ground surfaces. Typically, these vehicles have tires on which the vehicles are supported on the ground. These kinds of large vehicles are quite heavy, their weight of is distributed to a relatively small area by the vehicle the tires. As a result, the tires of such vehicles tend to compact the soil in the fields or other ground surfaces. Compacted soil discourages growth of crops planted in the fields which need loose soil to flourish, and ground surface compaction is often undesirable for other reasons as well.
In addition, since fields and other work sites are often wet due to rain or watering, vehicles which enter the fields become bogged down in the mud due to the fact that there is such a small tire area in contact with the ground. Therefore, it is highly desirable to develop a track apparatus for vehicles which disburses vehicle weight over a larger area so as to reduce the degree the ground compaction. Providing a larger ground-surface engagement area also serves to prevent vehicles from becoming bogged down in mud or other soft ground surfaces.
Prior track systems for vehicles are disclosed in U.S. Pat. No. Re 36,284 (Kelderman) and U.S. Pat. No. 5,829,848 (Kelderman), assigned to the assignee of the present invention and incorporated herein by reference. The Kelderman ""284 reissue and ""848 patents disclose track suspension systems for vehicles having a frame and a continuous rubber track. The drive wheel is attached to the frame for engaging and driving the continuous flexible track.
Each drive wheel of such prior apparatus has a plurality of drive projections disposed thereon which are between and engage corresponding rubber lugs extending from the inner surface of the flexible track. As the drive wheel rotates, the wheel projections engage the track lugs and drive the continuous flexible track. In such prior apparatus, the terminal surfaces of the track lugs do not engage the drive wheel; in other words, the track lugs are substantially unsupported. All of the driving force is imparted on the track lugs by the drive projections of the drive wheel, and this shear force, imparted as it is on substantially unsupported track lugs, tends to cause cracking and premature wear of the track lugs.
Certain prior art track apparatus, also of the type for use in place of a vehicle wheel, has a drive wheel which also includes side structure to retain the track lugs in engagement with the drive wheelxe2x80x94in an attempt to keep the track in proper alignment. In such prior apparatus, as with that described above, the terminal surfaces of the wheel lugs do not engage the drive wheel; in other words, the track lugs are substantially unsupported. Such drive wheels, as with those referenced above, impose shear forces on the track lugs, in the manner described above. However, when there is a tendency toward track misalignment, the side structure of the drive wheel engages the lateral surfaces of the track lugs, and imposes torsional and further shearing forces on such track lugs. These torsional and shearing forces exacerbate the resulting cracking and premature wear of the track lugs.
Consequently, it would be highly desirable to provide a drive wheel which does not damage the flexible track after extended use. Likewise, it would be highly desirable to provide a drive wheel which would minimize shearing forces on rubber track lugs and would minimize or eliminate the torsional forces described above.
It is an object of this invention to provide an improved track apparatus, of the type for use in place of a vehicle wheel, which overcomes some of the problems and shortcomings of the prior art, including those referred to above.
More particularly, it is an object of this invention to providing an improved drive wheel for engaging and driving the flexible track of track apparatus of the type for use in place of a vehicle wheelxe2x80x94namely, a drive wheel which overcomes the problems and shortcomings of the prior art referred to above.
Another object of this invention is to provide a track apparatus drive wheel which does not damage the flexible track during extended use.
Another object of this invention is to provide a track apparatus drive wheel which minimizes shearing forces on the lugs of flexible tracks used on such track apparatus.
Still another object of this invention is to provide a track apparatus drive wheel which minimizes or eliminates the torsional forces referred to above.
Yet another object of this invention is to provide a track apparatus drive wheel which effectively drives the flexible belt in difficult work conditions.
Another object of this invention to provide a track apparatus drive wheel which is simple and inexpensive to manufacture.
In accordance with the present invention, an improved drive wheel for track apparatus of the type mountable on the rotatable axle of a vehicle is provided. The flexible track of such apparatus, when mounted, has upper and lower lengths, and the drive wheel drives the track by engagement with the upper length thereof. The track has an main inner surface and a plurality of spaced lugs projecting therefrom. The lugs each have leading and trailing surfaces and a pair of lateral surfaces, and each lug terminates in a distal end which is a generally flat surface spaced inwardly from the main inner surface of the track. This invention deals with the configuration of the drive wheel and its driving engagement with the flexible track, and the configurations and features of the invention overcome the above-noted shortcomings and problems.
The drive wheel of the invention includes: a central hub portion mountable on the axle for rotational movement therewith; a radially-extending portion terminating in a circumferential edge; and a peripheral portion affixed to the circumferential edge and having (1) radially-projecting drive members defining lug-receiving gaps therebetween and (2) outwardly-facing lug-engagement surfaces positioned for engagement with the distal surfaces of the track lugs. The engagement of the distal surfaces of the track lugs with the drive wheel during operation, i.e., the engagement of the distal track-lug surfaces with the outwardly-facing lug-engagement surfaces of the drive wheel when the track lugs are in the lug-receiving gaps, serves to overcome the above-mentioned problems of unacceptable cracking and premature wear of track lugs.
In certain preferred embodiments, the peripheral portion of the drive wheel includes an outer rim which forms the outwardly-facing lug-engaging surfaces. In such embodiments, it is preferred that the outer rim include a plurality of spaced openings therein. The outer rim can be in a variety of forms, including a continuous form interrupted only by the radial projections therefrom which form drive members that engage the trailing surfaces of the lugs.
In certain other highly preferred embodiments, the peripheral portion includes peripherally-spaced cross-members affixed to the circumferential edge of the radially-extending portion of the drive wheel, and such cross-members form the outwardly-facing lug-engaging surfaces.
It is highly preferred that certain of such embodiments include a rigidity ring which has an outward edge parallel to and spaced from the circumferential edge of the radially-extending portion and that the cross-members be affixed to the outward edge of the rigidity ring to span the space between the rigidity ring and the radially-extending portion of the drive wheel. The rigidity ring and the radially-extending portion form open spaces therebetween between adjacent pairs of the drive members to receive debris during operation.
In very highly preferred embodiments, the drive wheel is substantially free of side structure in positions which are both laterally adjacent to the lug-engagement surfaces between adjacent pairs of the drive members and radially beyond the circumferential edge of the radially-extending portion of the drive wheel. With such highly preferred feature, the track lugs are free to adjust their precise positions of engagement with the lug-engagement surfaces during operation. This serves to minimize or substantially eliminate the harmful torsional forces discussed above.
In certain preferred embodiments of this invention, the outward edge of the rigidity ring and the circumferential edge of the radially-extending portion are formed with alternating aligned pairs of extended portions and aligned pairs of recessed portions. Each of the radially-projecting drive members is welded to one of the aligned pairs of extended portions, and each of the cross-members is welded to one of the aligned pairs of recessed portions. This facilitates manufacture of the drive-wheel of this invention.
This invention also involves a track apparatus of the type mountable on a rotatable axle of a vehiclexe2x80x94e.g., in place of an ordinary wheel, such as a tractor drive wheel. The track apparatus of this invention includes the inventive drive wheels as set forth above.